This project is concerned with the identification and purification of various cell membrane antigens from human lymphocytes with the prime objectives of (a) classifying human lymphocytes into subsets according to their immunobiological phenotypes; (b) revealing the cell membrane structures characteristic of each subset; and (c) investigating the characteristic cell membrane components for basic structure and functional significance. In order to do this we are involved in the isolation of individual antigens in large enough quantity for detailed studies of their basic structures and the production of required specific antibodies against various cell membrane antigens by conventional xenogeneic immunization and by the hybridoma technique. We are utilizing cells of established human lymphoid cell lines because they retain, in general, the membrane characteristics associated with cell differentiation, retain a variety of biological functions, and can provide sufficient homogeneous material for our investigations. We are particularly involved in the isolation of cell membrane antigens which are relevant to the transplantation reaction and also in the characterization of lymphocyte differentiation antigens which are relevant to classification of human lymphocyte subpopulations. Antibody reagents specific to those defined cell membrane components have found diagnostic application. It is possible that they would also find clinical application in modification of immune responses.